Just a few things to check… or try.
Using C:\Windows\System32\dxdiag.exe check that you have DirectX10 or better and WDDM 1.1, because 1.0 will not work, also be sure you have at least 4G memory!!
if that is all o.k. you can try to restart VS after deleting the AppData Folder (%LocalAppData%\Microsoft\Phone Tools) as suggested here.
However my solution is still not working …..